In 1805, while they were both sailing toward Libya, Jan met Solomon "Solo" Bolden, the Black Cross of the Templar Order who was at the time posing as a slaver. Despite finding him annoying, Bolden nevertheless accepted to protect Jan during his mission for Napoleon after the Flemish helped him fend off pirates sent by the Sultan to kill him. To secure Bolden's help, Jan also promised to help the Templar enter into the palace, the Sultan being behind the attempt on his life.

Once in the port city of Derna, the two men took camels and traveled to Tripoli, where they eventually met with the Flemish's contacts in a local tavern. There, Edmund, a deserter marines and Ahkbar, a shady local, revealed to them the existence of a secret underground tunnel used by the Sultans to discreetly smuggle precious cargo into the palace. Following the departure of their companions, Bolden and Graff bonded over several drinks with the Black Cross trying to learn what was "the diamond" mentioned by Edmund, until being interrupted by the latter being shot by guards in the street.

Later, they entered the tunnel after Graff picked the gate's lock but were confronted by several men waiting for them. During the brawl Ahkbar, who was in fact an agent of the Sultan, stabbed Bolden in the back. Subsequently, de Graff was thrown into the palace's dungeon where he met another prisoner who was revealed to be Bolden's predecessor, Tavis Olier.

During the three years they were imprisoned together, the old Black Cross trained Graff and inducted him into the Templar Order until one day on 29 July 1808, Olier heard that the Assassins were coming to buy the artifact in possession of the Sultan. In order to escape, the two Templars assaulted the guards bringing them food but Olier had to sacrifice himself to allow de Graff to accomplish their mission.

Graff as the Black Cross in 1808.

After dispatching several guards, the Templar finally reached Selim's apartment where he discovered that Ahkbar, who was an Assassin, had already poisoned the monarch and had taken possession of his prize, the fabled Koh-i-Noor. After revealing that he intended to betray the Brotherhood and keep the artifact for himself, Ahkbar tried to use the Koh-i-Noor and its power to create illusions, but Graff saw through it and killed him.

A group of Assassins quickly surrounded Graff but having heard Ahkbar's speech and after the Flemish told them that he wanted no part in their secret war against the Templars, they spared him and left with the box containing the artifact. However, Graff had lied about his commitment to the Order and had in fact removed the diamond from its box before giving it to the Assassins.

Shortly after he left the Barbary Coast and sought out Bolden's widow, informing her of Solo's exploits. The pair hit it off and after a night of passion, Graff fathered a child with her, who carried on the Bolden name. Their unanticipated coupling threatened to derail Juhani Otso Berg's pursuit of the Koh-i-nor in the 21st century when he was researching the Bolden bloodline with Graff's great-great-grandson André Bolden but the two managed to pickup the trail.

Exploring Graff's memories helped Dre deal with his PTSD following the Vietnam War and inspired him to reconnect with his estranged daughter.

van der Graff was a trained soldier, a skilled swordsman besting pirates as well as palace guards, he was also a skilled in lockpicking. After being trained by Tavis Oliver for over three years he became far more skilled, trained in stealth, unarmed combat. He was capable of throwing a sword directly into an enemy's chest. van der Graff also seemed to have enhanced his senses enough to best the illusions created by Ahkbar and sense the arrival of the assassins. van der Graff was also skilled in deception having managed to convince a team of assassins he had no loyalty to the templars. He was also fluent in arabic.